It is well recognized that ferrous metals can be cathodically protected against corrosion by being placed in an electrical circuit with metals which are above iron in the electromotive series, such as magnesium, zinc and aluminum. When two different metals are present in a corrosive environment, the oxidation of the metal which is highest in the electromotive series will occur.
To provide this type of cathodic protection, efforts have been made in the past to develop coatings for ferrous metals containing metal powder, such as zinc or aluminum. A difficulty lies in developing an appropriate vehicle or binder in which the metallic powder can be incorporated. The coating must be hard and abrasion resistant, and at the same time, adherent to the metallic surface so as to establish a permanent protective film which will not flake away or craze. In the past, various types of galvanic coatings have been proposed in which metallic powder, such as zinc, has been incorporated with a bonding agent, such as an alkyl silicate, and particularly ethyl silicate. However, these prior coatings have given extremely poor performance with respect to corrosion protection in a hot water environment of approximately 180.degree. F. to 212.degree. F., as encountered in a domestic hot water heater. At these high temperatures, the zinc particles not only oxidize and form carbonates, but the zinc particles will tend to polarize and lose their galvanic properties.